1. Field of Invention
The present invention relates generally to the field of computerized devices and data networking. More particularly, in one exemplary aspect, the present invention is directed to computerized interfaces, such as for example for self-synchronization of audio/visual (AV) entities.
2. Description of Related Technology
Presentation of audio and visual elements has a direct impact on customer satisfaction. For example, many multimedia devices are widely judged (and purchased) according to qualities such as: display quality, sound fidelity, smooth rendering, crispness of the display, etc. Other areas of multimedia applications which affect consumers include interoperation (e.g., with other equipment, legacy standards, etc.), ease of use, cost, etc,
To these ends, Audio/Visual (A/V) interface technologies have evolved from simple display logic circuits to complex systems capable of, inter alia, platform-independent operation, networked operation, etc. Moreover, current display interface technologies support seamless legacy display operation; newer functionality is layered over existing protocols. For example, secondary data may be transmitted during time intervals which are otherwise ignored by legacy devices.
DisplayPort™ is one example of a display interface technology referred to above. It is specified by the Video Electronics Standards Association (VESA). Current incarnations of the DisplayPort standard specify support for simple networking of digital audio/visual (A/V) interconnects, intended to be used primarily between an arbitrary assembly of multimedia “sources” (e.g., computers or CPUs) and “sinks” (e.g., display monitors, home-theater system, etc.).
Extant DisplayPort technology is an extensible digital interface solution that is designed for a wide variety of performance requirements, and broadly supports inter alia, PCs, monitors, panels, projectors, and high definition (HD) content applications. Current DisplayPort technology is also capable of supporting both internal (e.g., chip-to-chip), and external (e.g., box-to-box) digital display connections. Examples of internal chip-to-chip applications include notebook PCs, which drive a display panel from a graphics controller, or display components from display controllers driving the monitor of a television. Examples of box-to-box applications include display connections between PCs and monitors, and projectors (e.g., not housed within the same physical device). Consolidation of internal and external signaling methods enables the “direct drive” of digital monitors. Direct drive eliminates the need for control circuits, and allows for among other things, less costly and reduced profile (e.g., slimmer) display devices.
The current revision of DisplayPort (DisplayPort 1.2) transmits both control symbols and data symbols. Data symbols are scrambled in order to impart certain desirable characteristics, inter alia, provide DC-balance on the transmission medium, etc. Control symbols are not scrambled in this revision. Non-scrambled control symbols advantageously allow the comparatively rare control symbols to be instantly identified when received at, for example, a sink.
Additionally, current DisplayPort standards support flexible management of processors for generating display data. For example, DisplayPort systems support using a multiplexer (mux) to select between several GPUs (Graphics Processing Units); the currently selected GPU drives one (1) eDP (embedded Display Panel). Each time the mux switches from one GPU to another, the newly selected GPU must be synchronized with the eDP.
The scrambler state is specific to each GPU and is constantly changing; thus, during a switch the eDP must re-synchronize to the new GPU's scrambler. Without some information as to the scrambler's current state, the descrambler must wait for a known scrambler state to align its timing. Current implementations of DisplayPort periodically transmit a Scrambler Reset (SR) unscrambled control code for this purpose. Unfortunately, these SR signals occur very infrequently.
Experimental results have shown that prior art synchronization processes typically last approximately fourteen (14) milliseconds; however, worst-case operation can exceed twenty seven (27) milliseconds. Large switching delays can cause visual artifacts such as “bleaching”, “flashing”, etc. Humans can generally perceive visually unacceptable artifacts when transition times exceed sixteen (16) milliseconds. Thus, prior art solutions operate in a marginal range; a large percentage of transitions may detrimentally affect the perceived display quality.
Accordingly, improved apparatus and methods are needed to improve synchronization between devices being interfaced (e.g., two DisplayPort-enabled devices). Such improved apparatus and methods should ideally reduce synchronization times to acceptable levels for human perception of audio and visual content, even during worst-case operational conditions. More generally, such apparatus and methods would be useful to reduce synchronization times between peer entities for a wide array of audio/visual (A/V) applications.
Useful solutions should also seamlessly operate with existing protocols, messaging formats, etc. Such solutions would not add substantial additional messaging overhead, significantly decrease existing data rates, change message formats, etc., nor significantly impact existing system capabilities. Furthermore, useful solutions would permit backwards compatible operation with previously deployed legacy equipment, software, etc.